WASHINGTON—To hear Democrats tell it, Gov. Rick Perry's economic record in Texas is nothing more than a mirage and his views on Social Security make him "America's Most Dangerous Cowboy." In Massachusetts, President Barack Obama's allies say job creation lagged under Mitt Romney, whose policies would undermine the middle class.

Republicans won't pick a candidate to challenge Obama for months but Democrats already are working to poke holes in the two who, according to polls, are mostly likely to win the GOP nomination.

No matter who Republicans pick, the 2012 general election is all but certain to be negative given Obama's weakened standing and the sagging economy. Sharp contrasts between Obama and his GOP challenger are likely. And Obama's advisers stress that next year's election will be a "choice, not a referendum" on the president—a clear indication that the incumbent Democrat will draw bright lines between himself and the Republicans.

So Democrats are working to lay the groundwork for that choice now by highlighting the contrasts between Obama and the leading Republicans.

For now at least, the race to negatively define Perry and Romney in voters' minds is being driven by the Democratic National Committee and outside groups like Priorities USA and American Bridge, which formed following a 2010 Supreme Court ruling lifting the ban on corporate donations to political campaigns. The outfits are taking cues from Romney and Perry's tanglin over Social Security, health care and the economy, while working to cast the candidates as purveyors of tax policies that led to the economic downturn.

Most of the dirty work is being left to such groups, which helps insulate Obama and his campaign from criticism of waging a negative campaign more than a year before the election. Still, they aren't entirely innocent; the White House has poked Romney on the health care measure he signed into law in Massachusetts that was the basis for the federal program conservatives loathe.

"This used to be a Republican idea, by the way, this whole notion of the individual mandate, and suddenly some—it's like they got amnesia," Obama said during an August visit to Cannon Falls, Minn., referring to a "governor who is running for president right now."

In an interview earlier this month with NBC News, Obama declined to critique Perry. "Well, he's been the governor of a big state, and there's no doubt he's a credible candidate, as is Mr. Romney and a whole bunch of other folks," Obama said.

Democrats are challenging Perry's argument that his economic record in Texas would serve as a template to put the nation back to work while trying to portray him as out-of-step with most Americans.

Perry has highlighted his efforts to cut taxes in Texas and noted that since the middle of 2009, his state accounted for more than 40 percent of the nation's job growth. But Democrats counter that many of the new jobs in Texas are low-paying and the state benefited from high oil prices and more than $17 billion that Texas government agencies and businesses received from Obama's recovery act.

Beyond the economy, Democrats want to portray Perry as beholden to special interests and a cowboy who would make former President George W. Bush seem like a moderate. A web video by American Bridge calls him "America's Most Dangerous Cowboy" and shows a montage of clips in which the Texas governor refers to Social Security as a "Ponzi scheme" and a "monstrous lie on this generation." Democrats say the position could move seniors in their direction.

Romney, the former Massachusetts governor who founded a venture capital firm, is routinely painted as beholden to business interests who will change his position to suit his purposes.

Democrats hope to discredit Romney's work as a business executive by pointing to the Massachusetts economy during his tenure as governor and portray him as an out-of-touch corporate titan. Massachusetts ranked 47th in the nation in job creation from 2003 to 2007 under Romney's watch, beating only Rust Belt states like Ohio and Michigan, which lost thousands of manufacturing jobs during that time, and Louisiana, which suffered in the aftermath of Hurricane Katrina.

The DNC relished Romney's exchange with liberal activists at the Iowa State Fair last summer, when he declared that "corporations are people." And when Romney quipped in Tampa that he was "also unemployed," Democrats seized on it as being insensitive. In recent weeks, they have circulated reports that Romney was expanding his La Jolla, Calif., beachside home and promoted a video of Romney touring an Arizona Ford dealership, in which he told a dealer he has "a couple of Cadillacs at two different houses ... and I've got my Mustang."

Following Thursday's debate in Florida, Democrats pounced on another line from Romney—"There are a lot of reasons not to elect me. There are a lot of reasons not to elect other people on the stage"—to raise questions about Republicans' commitment to education, the environment and health care.

"The Republican candidates have repackaged the same economic policies that don't benefit the middle class and have been tried and failed," said Obama campaign spokesman Ben LaBolt.

Republicans call the strategy of sullying their top candidates an act of desperation, a sure sign that Obama will be hard-pressed to defend his record

"Because they have an unpopular candidate, the DNC and Obama campaign are trying to define the GOP candidates by going negative," said Republican National Committee spokeswoman Kirsten Kukowski. Instead of highlighting Obama's record, his campaign will try to tear down the Republican candidates' records "and attempt to ruin their personal credibility," Kukowski said.